1. Field of the Invention
The present invention relates to a method for bonding LCP and, more specifically, to a method for bonding LCP using an adhesive which has heat resistance and excellent adhesion to an LCP.
2. Description of the Related Art
An LCP (Liquid Crystalline Polymer) is attracting much attention even in the field of electronic materials because a highly elastic material is obtained when a molded product is produced therefrom and the LCP has high heat resistance and chemical resistance, due to the high crystallinity of the resin.
Meanwhile, an epoxy resin is widely used as a main raw material in the field of adhesives because a shrinkage of the epoxy resin is small when the epoxy resin is cured and it has excellent adhesion to metals.
However, it is known that a thermosetting adhesive typified by a general-purpose adhesive put on the market has poor adhesion to an LCP. For example, in case an LCP is used as a package material for electronic parts when the parts are mounted on a substrate, there is no thermosetting adhesive having sufficient strength obtained by bonding a substrate to a package. Therefore, its application field is very narrow at the moment.
In contrast to this, attempts have been made to enhance adhesion properties and improve bonding properties by the modification of an LCP itself (Japanese Patent Application Laid-open No. Hei 5-140431). However, this method in which 20 to 1 wt % of an alkylene ether is mixed on 80 to 99 wt % of an LCP impairs heat resistance that is one of the characteristic properties of the LCP and involves problems with solvent resistance and general applicability. Although the improvement of adhesion between an epoxy resin and an LCP by this modification is confirmed, thorough discussions have not been made on interface retention properties that is most important in adhesion between an adhesive and the LCP to be bonded. As an adhesive system having extremely low viscosity has been studied in the above application, the permeation of the adhesive into a molding resin is seen and it is considered that an anchoring effect is exhibited. However, the permeable adhesive is not preferred because it may change the characteristic properties of the LCP resin and the characteristic properties of internal electronic parts packaged with the LCP.
A method for bonding an LCP using a mechanical unit is also reported (Japanese Patent Application Laid-open No. Hei 5-177716). This method relates to a method in which the LCP is physically bonded by engaging or screwing. However, it is troublesome compared with a method using an adhesive, which is a defect of the method.
An adhesive having excellent thixotropic properties and low stringiness is reported, which is obtained by adding polycarbodiimide resin, water and a curing agent with an epoxy resin composition comprising an epoxy resin and a thixotrophy imparting agent and optionally a filler (Japanese Patent Application Laid-open No. Hei 9-53000). However, this publication doesn't say about its specific use and fails to disclose such an idea that it is an adhesive for an LCP.